The present invention relates to an electromagnetic flowmeter and a manufacture method of the same, and more particularly to an electromagnetic flowmeter of the type that a measuring tube is made of ceramics and measuring electrodes are not in contact with fluid to be measured, as well as a method of manufacturing such an electromagnetic flowmeter.
Electromagnetic flowmeters are designed on the basis of the Faraday's law of induction that when an electrically conductive fluid flows perpendicularly to a magnetic field, a potential in proportion to a flow speed of the fluid is generated in a direction perpendicular to both the direction of the fluid flow and the direction of the magnetic field. Thus, the flow rate of fluid to be measured is determined by applying a magnetic field to the fluid to be measured, which is flowing through a measuring tube, to generate a potential, and detecting the potential by a pair of measuring electrodes. There are two types of electromagnetic flowmeters; one type that the measuring electrodes are in contact with the fluid to be measured, and another type that they are not in contact with the fluid to be measured. Also, the measuring tube is primarily made of ceramics superior in resistance against corrosion and heat.
One of contactless electromagnetic flowmeters using a ceramic-made measuring tube is proposed in U.S. Pat. No. 4,539,835.
In the proposed electromagnetic flowmeter of the above prior art, the outer surface of a measuring tube is coated with a metal, i.e., metallized, using the vacuum evaporation method to form measuring electrodes and shields.
However, because the metal films formed by the vacuum evaporation method is weak in the interface adhesion intensity with ceramics, peel-off between the metal films and the ceramics gradually progresses at the interface when the measuring tube is repeatedly subjected to heat. Accordingly, there arise a problem that measurement accuracy is degraded or fluctuated.
With a view of solving the above-mentioned problem, an object of the present invention is to provide an electromagnetic flowmeter in which the interface adhesion intensity between metal films, forming electrodes and shields, and ceramics is increased to such an extent as not causing peel-off at the interface even if repeatedly subjected to heat, and which is stable in capability of measurement, as well as a method of manufacture of such an electromagnetic flowmeter.